This invention relates to earth boring. More specifically, this invention relates to a head for use with an earth boring machine operable to form generally horizontal passageways for conduits, cables, etc. beneath an established surface such as a roadway or the like without disturbing the roadway surface.
Underground conduits and the like are frequently placed by digging a trench to a desired depth, laying a continuous or articulated conduit within the trench, and then backfilling the trench. In some situations, however, it may be undesirable to utilize conventional pipe laying techniques. In this connection, it can be highly disruptive to traffice patterns to trench across an established roadway. Moreover, after conduit installation is completed, it is necessary to rebuild the roadway surface. This repaired strip is frequently subject to settling and/or wear damage that can create a potential traffic hazard. Further, in areas of high intensity piping such as a chemical processing plant or the like short run elevations in ground surfaces make piping installation by conventional trenching techniques difficult and burdensome.
In the above and other instances, it would be highly desirable to be able to form generally horizontal passageway beneath an established surface without forming a convention vertical trench.
In the past a number of machines have been designed to provide generally horizontal earth passages for relatively short distances. A specific disclosure of a highly advantageous hydraulic earth boring machine may be had by reference to applicants' copending U.S. application Ser. No. 06/151,865 entitled "Hydraulic Earth Boring Machine", filed May 21, 1980. The disclosure of this document is hereby incorporated by reference as though set forth at length. In general terms, however, earth boring machines are mounted within an excavated area or trench adjacent a roadway or the like. A relatively small rod carrying a conical head is then driven by the machine to pierce beneath the roadway surface to an excavated area or trench on the other side of the road. If the first pass does not produce a bore of large enough diameter for the intended purpose an enlarged reverse oriented head is fitted onto the piercing rod and the rod is drawn back through the bore to ream the passageway to a size suitable to receive an underground conduit.
The subject invention is directed to an earth boring head operable to be advantageously used as either a direct piercing head or, more frequently, as a return reaming head.
In the past solid conical bore head members have been frequently utilized. With these units, however, it is difficult to reliably produce a suitable sized bore because of the force necessary to drive the head through the earth. This problem is exacerbated when highly compacted or rocky soil is encountered. Moreover in shallow bores such heads have a tendency to "lump" pavement and crack concrete.
In other instances auger heads have been envisioned. Such units, however, are relatively expensive to produce and maintain and require somewhat sophisticated driving systems.
In another previously known system a slicing return head has been envisioned wherein radial slices are formed in a pilot bore by a return head. A third pass is then made to push the sliced material clear of the passageway.
Finally at least some systems have envisioned injecting water under pressure to cut through an earth formation. Such water boring equipment, however, tends to erratically exode voids in the bore and are frequently disapproved for use by local codes.
The difficulties suggested in the preceeding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness and operator satisfaction with prior earth boring heads. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that earth boring heads appearing in the past will admit to worthwhile improvement.